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7/16/2012 - 7/22/2012

Webinar Examines Livestock and Crop Options During Drought

Roger Elmore and Extension Field Agronomists, Department of Agronomy

Iowa crop and livestock producers dealing with drought–related issues are invited to attend an Iowa State University Extension and Outreach webinar Wednesday, July 25 to learn more about options available to them. County extension offices will be hosting the 1- 3 p.m. webinar. There is no charge to attend the webinar.

Livestock issues covered during the webinar will include options to help producers manage immediate needs related to stressed pastures and reduced hay supplies. “We also will talk about early weaning to reduce cow requirements and supplemental feeding,” said Dan Loy, Iowa Beef Center director. “Other topics facing producers are feeding value, proper ensiling and potential for nitrate toxicity for corn harvested as silage or green chop.”

Members of the extension crops team will cover the topics of crop growth and development under drought conditions and feeding drought damaged crops. “We will look at current conditions, short-range and long range forecasts, impacts of drought on forages and crops, and impacts on disease and insect development,” said Roger Elmore, extension corn specialist.

Farm finances
Extension specialists will discuss crop insurance coverage, grain marketing implications and valuing drought-damaged corn silage. Possible disaster programs related to the drought situation also will be covered, said William Edwards, extension economist.

Webinar locations
County extension offices are hosting the July 25 webinar. A list of host locations as of July 20 are shown at right. Extension agriculture and program specialists will facilitate the program at each site. Time has been allowed for questions and answers following the presentations. The webinar will be recorded and made available on the ISU Extension and Outreach website,


Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by e-mail at or 515-294-6655.

ISU Extension and Outreach Offers Iowa Drainage School

By Kapil Arora and Brent Pringnitz, ISU Extension and Outreach

Agricultural drainage is becoming increasingly important due to the critical role it plays for Iowa's emerging bio-economy. Drainage systems that are properly designed and operating are essential to achieving excellent agricultural production capability.

The Iowa Drainage School is being offered to address these issues on Aug. 21-23 at the Field Extension Education Laboratory (FEEL) between Ames and Boone, Iowa.

"People looking to install a new drainage system or retrofit an existing system will want to attend this school," said Matt Helmers, Iowa State University Extension agricultural engineer. "The workshop will focus on drainage design, economics of drainage, water management and legal issues related to drainage."

The intent of the Iowa Drainage School is to provide training about agricultural drainage concepts; planning and laying out drainage systems including surveying a profile, calculating tile line sizes and spacing using actual field data; and making connections and setting up drainage control structures. Regulatory considerations and fixing common drainage system issues will also be discussed.

Drainage contractors, landowners, professional engineers and consultants, NRCS professionals, county administrators and others who are involved in making drainage design decisions are invited to attend.

The three-day school featuresa combination of hands-on training, lecture and discussion, and problem solving using examples. By attending this school, participants will be able to plan and layout subsurface drainage systems and work out project costs.

Registration fees for this three-day school are $325 per person if registered by midnight, Aug. 10. Late registration is $375 and must be received by Aug. 17. Class size is limited to 40 participants and pre-registration is required. Registration fees include meals indicated on the agenda, refreshments and notebook.

Additional information, a detailed agenda and online registration are available at


Kapil Arora is an extension agricultural engineer. He can be reached at 515-382-6551 or e-mail Brent Pringnitz is an ANR Program Services coordinator. He can be reached at 515-294-6429 or e-mail

Yield Potential Slips as of July 15, 2012

By Roger Elmore, Department of Agronomy

In a July 7 ICM News article, I addressed two questions about corn yield potential through July 8 using Hybrid-Maize, a crop model. Yield potential through July 2 was not affected at any of the three locations modeled. However, yield potentials fell when the high forecast temperatures with no rain through July 8 were modeled. It’s time for an update on corn yield potentials.


What impact has the last few weeks of stress had on corn yield potentials?

It all depends on what kind of year we have from now through the end of the growing season.

  • Best-case scenario: Yields are reduced by 11 to 43 percent, depending on location (see Table 1). That means that if the best possible weather year (as recorded in the weather database at each location) occurs starting Monday, July 16, yields could be reduced by 11 to 43 percent from maximum yield potential modeled so far in 2012. 
  • Median-case scenario: If we have a year like that of the median year – that is half of the years yield more and half yield less – yields at the four stations with the longest weather database (NW, NE, C and SE) are reduced by 14 to 21 percent from the maximum to date for the  year.
  • Worst-case scenario: Yields are as good as, or better than, any previous year at two of the six locations modeled (NW and SW farms) and lower than the worst previous year at the other four farms (N, NE, C and SW farms). Neither the N nor the SW farms have had years with severe drought pressure in the weather database, which only goes back to 1997 at each of these farms.


What does this mean?

Although we have lost the top-end of yield at this point, the wide range of potential yields possible at each location provides hope that reasonable yields are still attainable - at least at these locations and with the assumptions I used in the model.


Current  Iowa corn situation

Monday’s Crops & Weather from USDA-NASS was discouraging but not unexpected. Iowa’s corn rates only 36 percent good to excellent and, on the other end, 27 percent poor to very poor. Three-quarters of our crop has silked. The short- and long-term forecast is for more heat with only isolated, pop-up thunderstorms, which may not provide much, if any, measureable precipitation. But, as many have said, “We’ll take what we can get!”

Although the crop condition erodes with every day of extra-high day and night temperatures with limited precipitation, a sizeable portion of the corn crop remains in surprisingly good condition. Reports from ISU Extension and Outreach field agronomists around the state mention that in most lesser-stressed fields, pollination and ovule fertilization went well and, thus, kernel numbers are good. We know that kernel number correlates positively with yield; more kernels, more yield. However, we aren’t out of the woods yet. Kernel abortion can and will occur – with stress conditions - through R3, the blister stage and, of course, kernel weight reduction can occur with stress all the way up to maturity. 


Model runs and assumptions

Hybrid-Maize uses historic weather data from automated weather stations. In this case, I used weather data from six of Iowa State University's Research and Demonstration Farms (see the tables). The model allows users to compare yield potentials given the weather actually recorded up through the simulation date. In this case, it included 2012 weather data through last Sunday, July 15. The model generates real-time yield predictions for the current season. What that means is that actual weather conditions up to the date of the simulation are, in a sense, considered the base from which to start. That is what we have to work with; unfortunately, we can’t change what has happened so far in 2012. The model assumes that there are no other limiting factors such as diseases, insects, low N availability, soil compaction, poor root development, etc. Only 2012 weather up to July 15 and historical weather plus the assumptions I made (Tables 2 and 3) affect yield predictions.

The model ‘asks’ a series of ‘what if’ questions.For example: What is yield potential if, from this day forward, we have weather conditions like those we had in the best possible year in the weather database for that location? What if the worst historical weather occurred?  Other scenarios are: 

  • 75 percentile, the year that yields more than 3/4 of the years in the database
  • Median, the year in which half the years had higher yields and half the years had lower yields
  • 25 percentile, the year that yields more than only ¼ of the years in the data base

The weather record begins in 1986, 1988 or 1997 for the individual Research and Demonstration Farms we’re working with here (Table 3).  Weather data used here comes directly from their automated weather stations. The limited years of data available at the Kanawha and Lewis locations are an obvious limitation to this type of analysis and interpretation.

Common inputs for all six sites modeled are provided in Table 2. Factors that varied across locations, such as soil textures, are shown in Table 3. Residue levels at planting, corn suitability ratings and other field-specific information are not factored into the analysis. However, some of the variability, especially in the early-season factors, is removed by using emergence date rather than planting date in the model. Soil moisture at planting was set at 75 percent field capacity for the topsoil and 100 percent for the subsoil. This was based on Hybrid-Maize runs conducted earlier in the year, which showed that differences in soil moisture status at planting had minimal impact on outcomes (see ICM News  Jan. 31, 2012) . These are similar assumptions reported in the July 7 ICM News mentioned above and referenced below.

For further information on Hybrid Maize and applications, see the following articles:

ICM News, Sept. 4, 2009
ICM News, July 7, 2012
University of Nebraska Crop Watch, July 10, 2012




Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by e-mail at or 515-294-6655.

Southern Rust Found in Central Iowa

By Alison Robertson, Department of Plant Pathology and Microbiology, and Erika Salaau-Rojas, Plant and Insect Diagnostic Clinic

Southern rust was reported in several fields in Butler and Grundy counties late last week. Leaf samples were received by the ISU Plant Disease and Insect Clinic, and confirmations were made. Because common rust is widespread in cornfields in Iowa, it is important for farmers and agronomists to correctly distinguish between these two rusts, especially if a fungicide decision is to be made.


Southern rust versus common rust

Southern rust can develop rapidly under favor able conditions (Table 1), and foliar fungicides are often required to protect yield. The earlier during the grain fill period that southern rust occurs, the greater the impact it can have on yield. Although we see southern rust in Iowa in most growing seasons, it is usually only reported in mid- to late August as the crop nears maturity. The outbreak of southern rust in central Iowa is unusually early, grain fill has just started, and, therefore, this outbreak is of concern. Furthermore, weather conditions in central Iowa at this time are very conducive to disease development (Table 1).

Common rust rarely impacts yield because most hybrids have very good tolerance to the disease, and conditions during grain fill are often too warm for common rust disease development (Table 1).  Thus, a fungicide application for common rust is not usually warranted to protect yield.



Hybrids vary in their tolerance to southern rust, so some fields will be more at risk than others. 

Previous cropping history and percent crop residue do not increase risk since this pathogen survives in the south and spores are blown up to Iowa each growing season.

Foliar fungicides are very effective against southern rust, but timing is important, especially if weather is conducive for disease development; applications should be made as soon as possible after southern rust is identified in a field or on susceptible hybrids within the area in which the disease has been reported.



Figure 1.  Common rust pustules are brick red, elongated and sparsely scattered on both leaf surfaces.


Figure 2. Southern rust pustules are bright orange, small and circular, and clustered on the top surface of leaves.



Update on Goss’s wilt and leaf blight

Goss’s leaf blight symptoms have been observed in our foliar product efficacy trials in southwest Iowa and central Iowa. Furthermore, ISU Extension and Outreach Field Agronomist Brian Lang reported Goss’s leaf blight on drought-stressed corn in northeast Iowa. The ISU PDIC has also received several leaf samples with Goss’s leaf blight. Farmers and agronomists are encouraged to continue to scout at risk fields for Goss’s. Please see this ICM News article, "Tips for diagnosing Goss’s leaf blight."



Jackson, T. A. 2008.  Rust diseases of corn in Nebraska. Nebguide G1680.


Alison Robertson is an associate professor of plant pathology and microbiology with extension and research responsibilities. You can reach her at 515-294-6708 or e-mail Erika Salaau-Rojas is a diagnostician in the Plant and Insect Diagnostic Clinic. You can reach her at 515-294-0581 or e-mail

This article was published originally on 7/23/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.

Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.